Telephone-exchange trunking system.



A. E. KEITH.

TELEPHONE EXCHANGE TRUNKING SYSTEM.

APPLICATION HLED AUG.28,1908. RENEWED DEC. 5.1914.

1,151,543; Patented Au 24,1915.

3 SHEETS-SHEET I.

I i 1 1 1 1 I mama;

A. E. KEITH.

TELEPHONE EXCHANGE TRUNKING SYSTEM.

APPLICATLON FILED AUG.28.190B. RENEWED 010.5.1914.

3 SHEETS-SHEET 2.

Patented Aug. 24, 1915.

. J (QM 99 I A'Zexmaz'lf. Fez

A. E. KEITH. TELEPHONE EXCHANGE TRUNKING SYSTEM. APPLICAHOH FILED 6.28.1908. RENEWED DEC. 5. m4.

1,151,543. Patented Aug. 24, 1915.

3 SHEETS-SHEET 3.

i NIH" 6 pig/mg 93 UNITED STATES PATENT OFFICE.

A LEXAICDEB. E. KEITH, 0F HINSDALE, ILLINOIS, ASSIGNOR T0 AUTOMATIC ELECTRIC COMPANY,.OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE TRU'NKING SYSTEM.

Specification of Letters Patent.

Patented Aug. 24, 1915.

Applitntion filed August 28, 1903, Serial No. 450,673. Renewed December 5, 1914. Serial No. 875,722.

To all 'zcizom it may concmz Be it known that I, ALEXANDER E. KEITH, a citizen of the United States of America, and resident of Hinsdale, Dupage county, Illinois. have invented a certain new and useful Improvement in Telephone-Exchange Trunking Systems, of which the following is a Specification.

My invention relates to telephone exchange systems of that particular character in which-one or more automatic trunking switches are employed for automatlcally establishing a trunking connection. for any suitable or desired purpose, such, for enample, as the establishmentofi. a tallnng'connection between andcalled subscribers in an automatic or semi-automatic telephone exchange system.

Generally stated thezobgect of my invention is the provision of an improved and highly efiicient telephone A special object is the .provisionoi antimproved and highly efli'cient trunkmg switch of such character that it' may he economically manufactured and installed atless expense than heretofore. p

To the foregoing and'other useful ends, my invention consists in matters hereinafter set forth and In the accompanying drawingsFlgm-e 1 is a side elevation of a'line switch embodying the principles of my invention. Fig. 2 is an end view ofthesame. Figs. 3 and- 4 are perspective riewsof detail parts. Figs. 5 and 6', taken together, represent diagrann matically a calling mbstafion A connected with :1 called substation A. in a stemembodying the principles of my invention.

As shown in Fi 1, the line switch or nonnumerical switch i is an improvement upon that disclosed in English Patent No. 26,301 or" 1906; By a non-numerical switch I mean a switch which operates independent of the digits of the called number, that'is, the operation of the said non-numerical switch is in no way dependent .upon' the numerical impulses corresponding to thedigit of the called number, in contradistinction to a numerical switch; such as a selector or con hector switch. The said switch lit-comprises the plunger 2vpivotally mounted upon-the curl of the plunger arm 3. It will be seen that the plunger arm 3 is in two sections; upon one section mounted the plunger,

and the other section 4 is adapted to rock or move about the point 5. These two sections are rigidly secured by the screw 6. This provision 1s made in order that the plunger arm may be adjusted so that the plunger 2 will properly enter the bank M. Upon the end of the section 4 there is mounted a thumb-screw 8 which is attached to the spi ralsprmgQ. Thisspiralspriugisinturn secured to the bracket 10. The thumb-screw and spiral spring arrangement admit of a proper tension adjustment for the plunger arm. Above the plunger arm there is a set screw 11 mounted in the bracket 12 for limiting the backward motion of the plunger 2. Themagnet'13 is divided into two sections 1% and 15. The sectionH comprises two a trip magnet winding and a bndge-cut-ofi wmdingzj The end 15 comprises-a line relay winding which controls the armature 16 When the winding on the end 15 is energized the armature 16 is attmcted and the spring 17 is pressed into contact with the .springIS. The bridge-cutofi' armature 19,:when attracted, shifts the spring '20 and 21 out of contact with the springs 22 and 18. In Fig. 2 there is shown a line switch L, and to the right a frame or mounting bracket 24 for a second line switch is shown. It will be-seen that those brackets or frames are stamped in groupsthatis, the frame for the'switch L, the frame 24, and still others 'to the right of thefframefl may be stamped and formed in one common piece such that when the line switches are ammbled on the brackets there is then a plurality of line switches mounted upon the common frame 25. At N (Figs. 1 and 2) there are shown the jacks or terminal connection for the (lifl'erent circuits of the switch, one of these sets of jacks N being provided for each line switch. The means for mounting the armatures of the line is best shown in Figs. 4 and 2. The bridge-cut-ofl armature 19 (Fig. 4) is adapted to rest in the notch 26 (Fig. 2), and the end 4 (Fig. 3) of the plunger arm rests on top of the cut-off armature 19 and in the notch 27. The line relay armature 16 at the bottom of the line switch magnet rests in the notch 28 and is retained in normal position by the coil spring 29. The magnet 13 of the line switch is retained in position by a key 31 which passes through an e e of the magnet bracket 32 after the bracliet has been passed through an opening in the frame. I

Since the bracket 32 which separates the two sections 1% and 15 is attached to the frame upon which the armatures of the switch are pivoted, the magnetic circuits of the two sections are separate and distinct. As regards the on the end 15, the air-gap between theup r end of the core and the armatnres 19 an 4 is short-circuited by the bracket 32, and consequently the en ergization of the winding on the section 15 serves to operate only the armature 16. Likewise, the energization of either of the windings on the end 14 afi'ects only the armatures and 19. Of the two windings on the end 14, the trip-in winding operates both the armature 19 and the plunger arm 4, while the cut-ofl' winding is stro v enough to operate only the armature 19. e cutofi' is not, however, strong enough to attract the plunger arm 4 out of normal position; but if this am is once operated it may be held in its operated position by this The master switch S (Fig. 5) which controls the plunger shaft 30 ofthe line switches may be of the general tyge disclosed in the Western Electrician of amnary 25,1908, and in the Amen'can Telephone Journal of May, 1968. The saidmaster comprises the usual motor magnet 33 adapted to operate the ratchet 'Wheel'34- which latter is in turn linked with the plungershaft. The master switch shown at O and comprises the individual segments a and the common segment 35. The wi r 36 is adapted to maintain some-one o theindividual segments a in electrical contact with the common-segment 35. The: motor magnet relay 3? is, as usual, arranged to close an energizingucirenit through themotor magnet 33. Rigi y secured to the ratchet wheel 34 is the fibe; intcrrupterh-l zkheel viii]: operates a pair 0 rings w arranged to close a en; through the motor magnet. In multiple with the motor magnet 33 is the open main relay 39 which controls the supply of current to the interrupter relays 40 and 41 which are provided for energizing the trip-in winding, as will be explained. The relays 39, 40 and 41 are slow-actingthat is, when the relays are once energized and the circuit then broken the armatures do not instantly retnrnto normal position, but remain in their energized position for a moment. These slow-acting relays 39. 0 and 41 are common to a group of line switch% in the same manner thatrthe master switch is common to a group.

The substations may be of any suitable or approved type. As shown, it will be seen that substation A is somewhat different frorn the usual automatic substation, said substation A being arranged and modified to operate in connection with a two-Wire system-that is, with a system in which no ground connection is used at the subscribers substation. Substation A, for example, comprises the usual received switch-hook 43, induction coil 44 which consists of the primary winding 45 and the secondary winding =16, transmitter 47, condenser 48, ringer 49, and impulse wheel 50 which has the usual impulse teeth 51. The impulse wheel 50 is secured to the shaft 52, to which shaft there is also secured the dial (not shown). when the dial is turned the impulse teeth 51 are adapted to engage the cam 53 upon the end of the spring 54 and thereby carry the latter out of engagement with the spring .55. Upon the switch-hook 43 there is secured the cam 56 which, when the switch-hook is up, permits the springs 57 and 58 to engage, thereby bridging across the subscribers line conductors 59 and 60 the primary circuit including the transmitter 47 in series with the primary winding -15; but when the switch-hook is lowered the spring 57 is carried outof engagement. with. the spring 58 and into engagementwith the spring 61, whereby the'riuger 49 in series with the condenser 48 is bridged across the line condoctors 59 and 60 instead.

The first-selectorswitch shown at E is of the general type described in United States LettersPatent No. 815,321, granted March 13, 1906, to Keith, Erickson and Erickson, and, as shown, is modified to adapt it to opcrate in connection with a two-wire common battery system. Among other details itembodies the following features: The switch shaft (notshown) carries the vertical and rotary wipers 61 and 62, respectively, and the private wiper 63. The side switch is well known and comprises the side switch wipers 64, 65, 66 and 67 which may he desas the vertical; rotary and private side switch wipers, and the rotary magnet wiper, 'vely. The side switch is under the control of the private magnet 68, and when said side switch is in normal or first position the wipers 64-, 65, 66 and 67 occupy the contact points 69, 70, T1 and 72, respectively; when in second position the wipers rest on the contact points 73, T4, 2'5 and 76, respectively; and when in third position the aecgntbact 77, 78, 79 and 80 are enga y enlre wi The windm' gs of the usuzil g fical and tary line relays are, in this case, combined into one double-wound relay 81 comprising the winding 82 which is connected with the battery lead 83, and also with the vertical trunk-line conductor, when the side switch wiper 64 is in first or second position. The second winding 84 is connected to ground, and also to the rotary trunk-line conductor, when the side switch wiper is in first or second position. Throigh the medium of this double-wound relay. and while the side switch is in first position, the subscriber controls the vertical magnet 85 which operates to raise the switch shaft and wipers 61, 62 and 63 vertically. The line relay 81 also controls the private magnet relay 86, which latter in turn. controls the private magnet: 68. As usual, the private magnet controls the side switch. While the side switch is in s cond position the rotary magnet 87 operates to carry the switch shaft and wipers GP, 62 and ($3 step-by-step in a rotary direction. The release magnet 88 provides means for restoring the selector switch to normal position. Upon the switch shaft which carries the wipeis 61, 62 and 63 there is mounted the arm 89 which, when the shaft is raised one or more steps. permits the spring 90 to engage the contact point 91, whereby the release magnet 88 is connected to the battery lead. The release relay 92 is pro vided for closing the energizing circuit of the release magnet 88 after the switch is op erased. Fin-thermore, the relay 92, upon energizing, provides an energizing circuit for the cut-oil relay winding of the line switch to maintain the line switch in its operated position. The relays S6 and 92 are slow-acting relays-that is, they are so'prt vided with a copper shield that when ener gized and the energizing circuit then broken, the said relays remain in an operated position for a moment or so. In other words, they do not instantly return to normal position after the energizing circuit is broken The connector switch H is a modified form of the connector switch disclosed in United States Letters Patent No. 815,176, granted March 13, 1906, to Keith, Erickson and Erickson. The connector switch shaft (not shown), like the switch. shaft of the selector, curries the line wipers 93 and 94 and a private wiper 95. The connector switch is also controlled by the calling subscriber through the medium of a double-wound line relay The line relay 96 is provided with the windings 97 and 98. One terminal of the winding 97 is connected to the battery lead, while the other terminal is connected with the vertical trunkdine conductor The winding 98 is connected withground and also with the rotary trunk-line conductor. This line relay fifidireclqly controls the vertieal magnet- 99. The purpose of'the' verti cal magnet 99 is to give the shaft and sha wipers a vertical motion, and the rotary magnet 16G- imparts to the shaft andshaft ipers a rotary or circular motion. The connector switch is also provided with the slow-acting release relay 100 which is the same as the release relay 92 of the first-se lectoiswitch. As usual, the private magnet; relay 4'9 controls the private. magnet 102', which latter controls the side switch wiper" 103, 104, 105, 106 and 107. The baclibridge relay 108, comprising the windings 109 and 110, provides the means whereby the called subscriber is furnished with battery current for talking purposes.

As here shown, my connector switch is of the automatic ringing typethat is, the sig naling of the called subscriber is not dependent upon the calling subscriber pressing a signaling button when he calls a line; for as soon as connection is established with the desired line the interrupter 111 intermittenfly closes an energizing circuit through the ringer relay 112, whereby the terminals of the ringer generator I are intermittently bridged across the normal conductors of the called line. The relay 113is so arranged that if a busy line is called the connector side switch is locked in second position, and the calling subscriber is given the busy-signal. The means whereby the connector switch may be restored to normal position is provided by the usual release magnet 11% which, when the connector switch shaft is miscd one or more steps, is connected to the battery lead through the normal springs 1-15 and 116. By means of the condensers 117 and 118 the circuit through theconnector switch is divided into two sectionsfThe busy signaling apparatus J comprises the mtefl-upter 119 in series with the winding 1:20 oftbe induction coil 121. The winding 122 with the spring 228, and when the relay 113 energizes, as will be explained, the busy-signaling apparatus is connected with the connector side switch wiper 103.

Tliecperation of my improred line switch maybe more clearly understood from an explanation of its operation when one subscriber operates the central oflice switches to establish connection with the line of a second subscriber. Itwill be assumed that the subscriber at substation A wishes to call the subscriber at substation A, to which latter is allotted the number 220. To call the numher 220 (substation A, Fig. '6) the subscriber at substation A (Fig. 5) removes his receiver from the switch-hook and operates the calling device for each digit in the wellknown manner-that is, when the receiver is removed from the switch-hook a preliminary impulse provides an energizing circuit for the trip-in winding of the line switch L,

whereby the line switch L is operated to seize an idle..ancl waiting or preselected trunk-line leading to a first-selector switch. The dial is turned for the first digit, and upon returning to normal position operates the first-selector switch to establish connection with an idle trunk-line leading to a con nector switch. In a similar manner the impulses delivered bv the dial for the last two digits are directed toward the connector H, which latter operates to place the shaft wipers in connection with the contacts corresponding to the desired station. The reliminary impulse for operating the e switch occurs when the receiver 42 is removed from the switch-hook 43 and the cam arm 56 permits the spring 57 to engage the spring 58, thereby removing the ringer from across the line and bridging the primary circuit instead. When the primary circuit is thus bridged across the line an ener circuit is completed for the line relay winding 124, said circuit extending from ground G through the springs 18 and 21 to the line conductor 59, through the primary circuit of the substation to the line conductor 60, through the springs 22 and 20, winding 12-1, through the winding of the interrupter relay 40, springs 125 and 126, springs 12? and 128 to the battery lead 83, thence through battery B to ground G. circuit includes two relay windings in series which opera-tively energize and attract their respective armatures, the relay 40 placing the springs 129, 130 and 131 in contact, and the armature 16 placin the springs 17 and 18 in contact. When &is operation of the windings 40 and 124 occurs, an energizing circuit is established through the trin in 132 from ound G through the springs 18 and '17, winding 132, springs 131, 130 and 129, springs 12? and I2S to the battery lead 83, thence through battery B to ground G. Also, when therelay 40 energizes, a circuit is closed through the interrupter relay 41 extending from ground G through the relay 41, springs 130 and 129, springs 12? and 128 to the battery lead 83, thence through battery B to ground G. "The-relay 41, upon energizing, operates to disengage the springs 125 and 126, where by thecircuit through the line relay winding 124 in saris with the interrupter relay 40 is broken. This permits the two relay armatures to restore their respective springs to normal position. Furthermore, when the trip-in winding 132 becomes energized, as explained, the mature 19 and the plunger cm? are attracted against the core. The attraction of the armature 19 rsults in the separation of the springs 20' and 22, and 21 and 18, whereby the line conductors 60 and 59 are disoonnmted from the line switch springs 20 and 18.

When the plunger 311113 is attracted the plunger 2 is thrust into an idle bani; tenninsl. pre sing the following springs into contact: 133 and 1:31, 135 and 136, 137 and 13S, and 1539 and 110. The engagement of the springs 133 and 13% and 139 and 149 extends the subscribers line conductors 59 andGO to the line relay S1 of the first-selector switch E. when the bank springs 1-37 and 138 engage, an energizing circuit is established through the motor magnet relay 37, which latter in turn o'perates to close an energizing circuit through the motor magnet 33 of the master switch S. The motor magnet then operates to advance all idle plungers that are in looking engagement with the shaft to a point opposite the next idle bank terminal similar to the terminal just engaged. The circuit through the relay 37 extends from ground G through the winding of the relay 3'? to the common segment 35, thence through the wiper 36, through the segment 141, conductor 142, bank terminal springs 13? and 138, through the winding of the common resistance coil 143 to the battery lead 83, thence through battery B to ground G. The relay 37, upon energizing, operates to place the springs 1&4 and 145 in contact, whereby a circuit is completed through the motor magnet said circuit extending from ground G through the winding of the motor magnet 33, interrupter springs 14? and 146, motor magnet relay springs 144 and 145 to the battery lead 83, thence through battery B to ground G. The motor magnet 33, upon energizing, attracts its armature 14S, whereby the pawl engages the ratchet wheel 34, advancing the latter one step. When the armature 1-28 is attracted against the magnet cores the springs 146 and 1-17 disengage, thereby breaking the energizing circuit through the motor magnet 33 and permitting the armature 148 to return to normal position. When the ratchet wheel Si is given one step the fiber wheel permits the springs 149 and 150 to engage, thereby closing a new circuit through the motor magnet- These springs 149 and 150 maintain the circuit throl h the motor magnet until the next suc 'ng tooth on the fiber wheel 38 permits the springs 149 and 150 to disengage; but by that time the n1:1ster switch bank wiper 36 has reached the next individual segment 151, and if the trunk corresponding to this trunk is busy a new circuit is closed through the motor magnet relay 37, which relay again operates to close a circuit through the motor magnet 33 which also again operates, as previously explained. This operation of the master switch continues as long as the master switch bank wiper 36 continues to find individual segments 0 upon which there are guarding potentials As soon as an idle segment is found, however, the energizing circuit through the motor magnet relay 3? is broken. at which time the said relay in turn breaks the energizing circuit for the motor magnet 33 until the next subscriber calls. The open main relay 39, as previously stated, energizes in multiple with the 130- tor magnet and, when energized, main battery (the non-groimdcd pole of the hattery) is disconnected from the interrupter relay 40. This provision is made in order that no line switch of the group may be tripped-in while the master switch is opcrating to select an idle trunk. \Vhen the bank springs 135 and 136 engage, an energizing circuit is established through the bridgecut-olf winding 152 extending from ground G at the first-selector E, as will be explained, through the springs 153 and 154, over the private trunk conductor 1-55, through the bank springs 136 and 135, through the bridge-outwit winding to the battery lead 83, thence through battery B to ground G. The bridge-cut-otf winding thereupon energizes the magnet core an maintains the plunger arm 3 in its attached position. The engagement of the bank springs 13:) and 136 also establishes a arding potential by way of the norma conductor 156 to the connector rivaie bank contacts corresponding to the ine that terminates in the line switch L to prevent any subscriber from calling the said line after the calling subscriber at substation A re moves his receiver preparatory to making a call. as explained. Also, the closure of conneftion between the springs 137 and 13S establishes a guarding potential at the master switch bank contact 141. It will be understood that the said bank terminal (the one just engaged), being the first bank terminal of the line switch bank, 00 nds to the first segment 141 of the master switch bank and. therefore. to the trunk-line the conductors 157, 158 and 155 of which terminate in the first selector switch E. This guarding potential protects the seized trunk conductors 157. 158 and 155 from being seized by other plunger-s, as already explained.

The closure of connection between the springs 133 and 13! extends the calling subscribers line conductor 59 to the trunk eonductor 15? and the side switch wiper 64 of the firs-selector switch E. The closure of contact between the springs 139 and 140 in a similar manner extends the subscribers line conductor to the trunk conductor 158 and to the side switch wiper 65 of the selector E. The subscriber has thus established connection with the selector switch, which is now operated by the impulss that are delivered when the dial returns to normal position for the first digit. The operation of the switches up to this point has occurred before the snbscriber releases the dial for the first digit. When the subscribers line conductors 59 and 60 are thus extended to the first-selector switch wiper 64, contact point 69, through the winding 82 to the battery lead 83, thence through battery B to ground G. The relay 81, upon energizing, operates to place the springs 161 and 162 in contact, whereby an energizing circuit is established through the release relay 9'2 extending from ground (l through the springs 161 and 16:2, relav 92 to the battery lead 83, thence through battery B to ground G. The release relay 92, upon energizing, operates to carry the spring 163 out of engagement with the spring 16% and into engagement with the spring 165, and the spring 153 into engagement with the spring 154. This is the condition of the first-selector switch E when the subscriber operates the dial for the first digit. The first digit being 2, the impulse spring 54 is twice carried out of engagement with the impulse spring 55. As a result the energizing circuit through the line relay S1 is broken twice, and the spring 161 comes into contact with the spring 166 twice. After the two impulses are thus transmitted, the line relay 81 again energizes and carries the spring 161 into contact with the spring 162. As previously explained, the relay 9-2 is slow-acting-that is, slow to deenergize; and when this energizing circuit is momentarily broken during the vertical impulses just. delivered, thesaid relay does not deiinergize, but remains in an opemted position with the spring 163 in contact with the spring 165. Then when the spring 161 engages the spring 166 two impulses are transmitted. to the vertical magnet 85 from ground Gr through the springs 161 and 166 to the springs 163 and 165, through the privatemagnet relay 86, through the winding of the vertical magnet 97.;contact-point 72, side switch wiper 67 to the battery lead-83. thence through battery B to ground G. Tw'o impulses being transmitted, the vertical magnet 85 is thereby energized twice, and the shaft wipers are given two vertical steps in the well-known manner. It will be seen that the private magnet relay S6 is included in the energizing circuit of the vertical magnet 85. The relay 86 also energizes, but being a slowaeting relay it energizes on the first impulse and remains so until the impulses are trim..- mitted. relay, upon energizing, operates to close the springs 167 and 168 in contact, whereby an energizing circuit is established through the private magnet 68. This circuit extends from ground G through the springs 167 and 168, private magnet 68 to the battery lead 83, thence through battery B to ground G. The private magnet relay 86 deenergizes after the last vertical impulse, since the energizing circuit is no longer maintained after the springs 161 and 166 disengage. Hence the said relay deenergizes, permitting the springs 167 and 168 to disengage, whereby the energizing the rotary magnet 87 were ({Xtended to the first selector.

circuit through the private magnet 68 is in turn broken. which magnet now decnergizcs and permits the side switch to pass from first to second position, thus permitting the side switch wi rs 66 and'67 to engage the contact points 5 and 7 6, respectively.

The closure of contact between the side switch wiper 67 and the contact point 7 6 sets up an energizing circuit for the rotarymagnet 8'? from ground G through the 1nterrupter springs 169, through the windlngof the rotary magnet 87, contact point 76, side switch wiper 67 to the battery lead 83, thence throughbattery B to ground G. The said rotary magnet then operates to rotate the shaft wipers 61, 62 and 63 of the selector E into engagement with the first contact of the second level of the selector banks, from which contact it is assumed the trunk-line conductors 170, 171 and 172 lead to the conhector switch H. If the first trunk-line is busy, however, and the wipers have to pass over busy trunk-lines, then as soon as the private wiper 63 engages the first private bank contact the private magnet 68 age-1n energizes locking the side in second position. The energizing circmt for said private magnet extends from and G, springs 174 and 176, conductor 14 through the private wiper 63, thence through the conductor 17 3 to the side switch wiper 66, contact point 75, through the win a of the private magnet 68 to the battery cad S3, thence through battery B to ground G. The private magnet 68, upon thus becoming energized, locks the side switch wiper 67 in engagement with thecontact int 76, whereby be energized to operate the mechanism step-by step-until the are carried beyond" the last busy trunk-line At the instant that the private wiper leaves the last busy contact point the energi circuit through the private magnet 68 is estroyed, and as a result the selector side switch passes to third position. If, however, there are no busy trunk-lines, the private magnet 68 releam the side switch to third position as mu as the wipers are carried into engagement with the first trunkline. .As soon as the side switch asses to third position, as stated, the subscri rs line conductors 59 and are extended to the conductors I70 and 171 which, in this case, it is assumed lead to the connector switch H. The extending of the line occurs, of course, as soon as the side switch wipers 64 and engage the contact points 77 and 7 8, respectively. when the subscribers line con ductors are thus extended to the connector switch H an energizing circuit is established through the line relay 96 in the same manner in which the energizing'circuit was established through the line relay S1 of the se lectqr switoh 15' when the line 00l1$16l30r8 ergizing circuit through the line relay 96 extends from ground Gr through the winding 98, trunk conductors 171 and 158 to the line conductor 60, thence through the substation to the line conductor 59, trunk conductors 157 and 1T0, thence through the winding 97 to the battery lead 83, and through battery B to ground G The line relay 96, upon energizing, operates to shift the spring 17d from the spring 175 to the spring 17 6, whereby an energizing circuit is established through the release relay 100 extending from ground G through the springs 174 and 176, relay 100 to the battery lead 83, thence through battery B to ground G. When the relay 100 energizes, the spring 177 is shifted out of contact with the spring 178 and into contact with the spring 179, and the spring 180 is shifted into engagement with the spring 181. This primary operation of the connector relays 96 and 100 occurs at the instant that the side switch wipers 6i and 65 of the selector E pass to third position and extend the subscriber's line conductors to the connector H. The engagement of the springs 181 and 180 establishes a guarding potential for protecting the trunk-line conductors 170, 171 and 172 against seizure by another line and first-selector switch. This potential extends from ground G" to the side switch wiper 105, springs 180 and 181, conductor 172 to the private bank contact engaged by the shaft wiper 63. Furthermore, when the side switch of the selector E passes to third position a new energizing circuit is established through the release rclay 92, said circuit extending from ground G" at the connector switch to the conductor 172, through the shaft wiper 63, side switch wiper 66', conductor 182, through the release relay 92 to the battery lead S3, thence through battery B to ground G.

The operation of the dial for the last two digits afiects the connector switch, and when the dial is operated for the second digit 2 the impulse spring 54 is twice carried out of engagement with the spring 55, thereby momentarily denergizing the line relay 96 twice, whereby the spring 174 twice ngages the spring 175, thus sending two lmpulses to the vertical magnet 99 from ground G through the springs 1H and 175. springs 17'? and 179, through the vertical magnet 99, side switch wiper 106, private magnet relay 101 to the battery lead S3, thence through battery B to ground G. The private magnet relay 101 energizes when the first impulse is delivered, and since the said relay is slow-acting it remains in an operated position until all the vertical impulses are sent. The vertical magnet, upon being energized, operates one step at a time to carry the shaft wipers 93, 94 and 95 two steps to a pointopposite the second level. The relay 101, upon energizing, shifts the spring 183 out of engagement with the spring 18% and into engagement with the spring 185; also, thespring 1S6 is-shifted out of engagement with the spring 185. When the springs 185 and 183 engage, an energizing ci rcnit is established through the private magnet 102 from ground G through the springs 185 and 183, private magnet- 102 to the battery lead 83, thence through battery B to ground G. The relay IGLheing a sow-acting relay, remains in an operated position while the. vertical im pulses are being sent; but after all the impulses are delivered, and the-line relay 96 returns to its operated position, the circuit through the relay 101 becomes broken, thus permitting the springs 183 and 185 to ren-n to normal position. When the springs 13? and 185 disengage, the circuit through. the private magnet 102 becomes broken, whereby the said magnet deenergizes, permitting the side switch to pass from first to sewnd position. The calling subscriber now opemtes the calling device for the last digit 0. thereby transmitting ten impulses and operating the line relay 96 ten times. Each time that the. line relay springs 1'74 and engage. an energizing circuit is established through the rotary magnet 100 from ground G through the said springs 174 and 13. and through the springs 17? and 179, locking relay springs 18? and 188, through the rotary magnet 100*, thence through the side switch wiper 106, and through the private magnet relay 101 tothe battery lead 83, thence through battery B to groundrG. A gain the private magnetrelayenergizes, as in the pre'riouscase. remaining so until all the irnpnlses are transmitted, thereby retainin the private magnet energized also; The rotary magnet 10:3 then operates to rotate-"- the shaft wipers into engagement with the desired line If this line-isbusy at the time, the connector side switch will be lmked in second position in a manner to-b'e described, and the chi ling subscriber is given the busy-signal. thus making it impossible to extend the collin-g line into connection with the called line.

Before describing the results thatfollow when the connector finds a bus? line, the cles 'iption of how a connection is established will he completed. As soon as the line relay 96 L to operate for-the last digit,

I the private magnet relay. 101 denergizes, as

heretofore explained, in this instance permitting the side switch to trip toth rd [JO-51;"

tion. The resnlt is that 'the side switch vn'pelrs 1G3, 194-. 105. 106 and 10? engage the contact points: 189, 190. 191, 192 :md'193, respecti'iely. Then the side-switch wiper 1Q? engages the contact point 193 a guarding potential is completed at theprivatc 9 for protecting the seized line against outside interference while the connection is es tablishecl. This guanling potential extends from ground G to the Contact point 193, thence by way of the side switch wiper 107, lockin -relay springs 191 and 195 to the private wiper 95. Not only does this guarding potential prevent other connectors from seizing the same line over multiples of the normal conductors 196, 197 and 198, but it also provides means for energizing the bridge-entail relay winding 199 of the line switch L, whereby the switch L is prerented from operating when the called subscriher removes his receiver 200 from the switch-hook 201. It will also be seen that when the side switch passes to third position the trunk-release conductor 172 that runs between the firstselector and the connector is provided with guarding potential from ground G through the line relay springs lT l'and 176 to the conductor 17:2. ever, while-the side switch is in first or secend position a guarding potential for this trunk conductor 172 is also provided from ground 6 but through the side switch wiper 105, release relay springs and 181. The reason for this is that the guarding potential from ground G is interrupted while the line relay 96 is operating, and there is some liabilityiof some other selector similar to the first-selector E stopping on the same trunk-line. After the side switch passes to third position, however, there is no such liabilitg ancl the potential 'is provided from ground =G through the line relay springs, as stated. wipers 103 and 104 engage the third-p -1- tion contact points 139 and 190, the calling subscrihers line is placed in connection with the called suhscribers line over the heavy conductors shown, pa$ing through the ringer relay springs 202 and 203 on one side, and Qllland 205 on the other side. As soon asconncction is thus established the ringer relay 112 is energized over the circuit established when the side switch wiper 106 can gages the contact point 192, the energizing current flowing from ground G through the intemipter 111, through the back-bridge relar spr ngs 206 and ringer relay 112,

conductor 20S. contact point 19-2, side switch I wiper 106. private magnet relay 101 to the battery lead 83, thence through ba ttery B to ground G.

It will be seen that as the interrupter 111 revolves, the energizing circuit of the ringer relay 112 will be broken periodically, so as not to ring the called subscriber continuously. It will be seen that each time that the ringer relay is energized the springs 20?, and are separated from the ringer relay 20-2 and 204, therebfvbreali ng the calling line from the called line, and pressing the springs 203 2111:1205 onto the springs 209 and 210, which latter are the terminals of the ringer generator I. As a result ring- How- Of course, when the side switch ing current is sent over the called line for energizing the bell 211 while the springs 212 and 213 are in contact. The guarding potential from ground Gr to the shaft wiper 95 also'provides an energizing circuit for the bridge-cut-ofl winding 199, said circuit extending frornground G to the wiper 95-, as traced, through the conductor 198, winding of the bridge-cut-ofi' relay to the battery lea? 8 3, thence tlnl'p B to ground I. The strengt o e magnetism produced by the bridgocut-ofi winding is not sufiici'ent to attract -theplnnger arm and thrust the plunger into a' bank terminal. The bridge-cut-ofi' armature 21-31, however, is sin-acted and the bridge-cut-ofi springs separated. thereby disconnecting the subscribers line conductors 215 and 216 from the line switch L. The ringer relay continues to energize intermittently each time that the interrupter 111 closes the circuit. Howeser, as soon as the called subscriber answers, the back-bridge relay 108 is energized by a flow of current from ground G, contact point 193, side switch wiper 10?, winding 110 of the back-bridge relay 1G3. ringer relay springs 204::md 205, side switch wiper 16%, contact point 190, line wiper 9-1. normal conductor 19?, line conductor 216, switch-hook springs 213 and 21?, impulse springs 21S and-2195 transmitter 229. line conductor 215, normal conductor 19$ line wiper 93, contact point 189, side switch wiper 103, ringer relay springs 203 and 992, winding 109 of the back-bridge relay 108, thence to the battery lead 83; and through battery B to ground G. when the back-bridge relay 108 is once energized, howerer, the energizing circuit for the ringer relay 112is interrupted at a point between the springs 2G6 and thus making it imposible for the ringer relay to energize as long as the called subscriber is on the line. The subscribers thus connected maycommunimte over the main talking conductors indicated by the heavy lines and including on one side the condenser 11'? at the connector H, and on the otherside the condenser 118. After the subscribers are through talking, if the calling subscriber hangs up his receiver he opens the line circuit at a point between the springs 57 and 58. thereby initiafing the release of all the switches. This release is as follows: When the circuit is broken betwam the said springs 57 and 5S the double-wound line relay 36 and the release relay 100 of the connector H dene The denergization of the slow-act'mg relay 100 and the line relay 96 closes the energizing circuit-for the release magnet 11% at points the springs 11? and 17S and between the 174 and 175. A flow of current is, therefore, set up from ground G through the springs 171 and 175, through the springs 177 and 178 to the release magnet 114, thence through said magnet to the oif-normal spring 115, to the contact point 116 and to the battery lead 83, thence through battery B to ground G. The release magnet instantly releases the connector switch shaft and side switch, thereby breaking the energizing circuit through the back-bridge relay 108, if the called subscriber has not in the meantime restored his receirer, and also the energizing circuit through the bridge-cut-ofi relay 199 of the called line switch L. As soon as the connector switch shaft reaches its lowest position it breaks the circuit for the release magnet 114 by separating the oilnormal spring 115 from the contact point 116, at which instant the release magnet of the connector is also restored. The operation of the line relay 96 and of the slowacting relay 100 not only causes the release of the connect-or, as described, but also the release of the p switches, because the ground connection omground G to the mink-release conductor 172 is interrupted by both of these relays Since the release relay 92 is dependent upon this ground for its energized condition. as already explained, it follows that it will fall back, with the following results: As soon as the release relay 92 of the first-selector E deenergizes, the spring 163 falls back into normal engagement with the spring 164, thereby closing an energizing circuit for the re lease magnet- 88 from ground Gr through the springs 1 61 and 166, through the springs 163 and 161 to'the release magnet 88, thence to the contact point. 91, off-normal spring 90 to the battery lead 83, thence through battery B to ground G. As soon as the release magnet 88 energizes, the first-selector side switch and switch shaft are restored, which latter, upon reaching its lowest position, opens up the release circuit at a point between the oil-normal spring 90 and the contact point 91, whereby the release magnet 88 is restored also. Furthermore, when the rfilease relay; 92 tigcnergiies and separates t e springs 153 an 154, t e energizi' 'ng circuit through the bridge-cutoff 152 of the line switch L 15 broken. hen this circuit becomes broken the magnet core de energizes and permits the plunger arm 3 to return to normal position and withdraw the plunger from the bank terminal. After the switches are thus restored the calling subscriber can. of course, then proceed to make another call.

Returning now to that stage of the call where the calling subscriber was operating the connector switch in accordance with the 7 last digit 0, it will be explained What takes place in the event that the desired line is busy. When the line #220 is calling, or when ithns been called by someone, the prirate bank contacts in which the normal con ductor 19S terminates are connected to ground. If another connector switch has called the line this guarding potential is supplied through the connector switch from a ground terminal similar to the ground terminal G in the connector switch H, as already explained; but if the line switch L iscalling, aguarding potential is established from the first-selector release relay ground, as in Fig. 1, thence to the private bank contact. Therefore, when the subscriber at sub station A sends in the last impulse the prirate wiper 95 is carried onto the grounded contact; and when the slow-acting relay 101 of the connector denergizes, instead of the side switch tripping to third position, as in the case where the line is not busy, it is locked and the calling subscriber is then given the busy-signal. The method by which this side switch is locked is as follows: The slow-acting relay springs 183, 184 and 185 are so arranged that as the relay 101 denergizes, the spring 183 engages the spring 1% before it leaves the spring 18:}. and in this way the private magnet is prevented from denergizing, because the spring 181 is connected with the private wiper at the time over the following circuit: from the private 95 to the locking spring 195, thence to the spring 194,;and through the winding 1100i the backbndge relay 108 to the talking line conductor 221, thence through the ringer relay springs 2M and 205 :to the side switch 104, contact point 222-'{the side s'witch being in second position) to the slow-acting relay spring 18;. Therefore, when the spring 183 cugagw thespring 181 the private magnet 102 is not denergized, since the energizing C11- cuit is from the private wiper 95 to the said spring 184, as described, thence through the spring-1S3, and through the prirate magnet 102 to the battery lead 83, thence through battery B to ground G. The private magnet therefore remams energized, re the sideswitch in second position. It will seen thatat the sametime the back-bridge relay 108 energizes in series with the private magnet 102 over this circuit from the private wiper -95. Thercfore, the

back-bridge relay 108, upon energ1z1ng,-

presses the springs 223 and 29% intqcontnct, thereby the locking relay 113 over the. following circuit: from ground G through the slow-acting relay springs 185 and 186, through the private magnet springs 225 and 226, throu the said relay 113, and through the backridge relay springs 223 and 2-24 to the battery lead 83, thence through battery B to ground G. It will be calling subscriber from further rotating the connector switch if he should attempt to operate his dial while receiving the busysignal-that is while the connector switch is locked in second position. It will also be seen that when the relay 113 energizes, the circuit for maintaining the private magnet 10'2 energized is shifted from the private wiper 95 to the spring 227, which latter is connected to ground G. The object of this arrangement is to prevent the side switch from unlocking and posing to third position, if the switch that is maintaining the called line busy should be releaad while the calling subscriber A (Fig. 1) is receiving the busy-signal. It will be evident that if the ground (3: were not substituted for the ground at the private wiper 95, the private magnet 102 would denergize if the switch that is supplying round at the private wiper 95 should re case, which would, of course, be undesirable. It will also be seen that the relay 113, upon energizing, closes the springs 228 and 123 in contact, thereby establishing the busy'circuit as follows: from the secondary winding of the busy coil 121 through the springs 22S and 123 to the acond-position side switch contact point 29, side switch wiper 103, ringer relay springs 203 and 2%, through the condenser 11?, through the substation A to the other side of the line, then over this side back to the connector H, through the winding 98 of the line relay 96 to ground G to the interrupter ground Gr, through the interrupter 119 to the primary of the busy coil 121and back to the secondary winding. when the calling subscriber rccei es the busy-signal he understands that the line is busy and hangs up his receiver. The line circuit is open, as already explained, with the result that the line and slow-ac relays 96 and 100 of the con ncctor H energize, causing the release of the connector and all other switches, as heretofore explained. It will, of course, be seen that as soon asthe side switch is restored the energizing circuit for the back-bridge relay 108 (which includes the winding 110 thereof) and for the private magnet 102 is broken, when the side switch wiper 104 leaves the contact point 222. Now, since the energizi circuit for the locking relay 113 is contro ed by the back-bridge relay 108, the said locking relay is also denergized, and the connector switch is leftin normal condition.

Heretofore the windings of the difl'erent relays and operative magnets of the line switches have been upon separate or indi- \"idual spools and cores, but in my present switch all of the windings are wound upon the same spool and core and are so arranged that each performs its proper function without interfering with the others. When the winding 124 carries current the armature 16 alone is affected thereby; also, when the bridge-cut-ofi winding, which is wound upon the same end of the core with the trip-in winding 132, carries current the bridge-cutofi' armature 19 is attracted against the magnet corc, and the springs it controls are separated, but the plunger arm is not operated; but when the tripdn winding 132 carries current the magnetism produced in the core is sufiicient to attract the armature 19 and also the plunger arm 3, which latter in turn thrusts the plunger into the bank. When the plunger enters the bank an energizin circuit is closed through the bridge-cuto winding 152. The magnetism produced in the core by this winding is ample to maintain the plunger arm in its attracted position after bemg operated by the trip-in winding 132.

From the foregoing it will be seen that I provide a two-wire automatic telephone exchange system in which there is only a smgle magnet spool for each subscribers line, the energizing of which magnet is controlled by the subscriber over a complete metallic line circuit. The said spool, it will be seen, has one winding which is energized over the complete metallic line circuit, another winding which is energized over a. local circuit, and a third winding which is energized over a third trunk conductor extending to the next switch. The single spool thus r0- vided is suflicient, however, to effect a of the desired operations of the subscribers line or tnmking switch. Asshown, the said line or trunking switchL is allotted to a subscribers line, but it will be readily understoodthatitisnotlimitedtosuchmas it may also be used for extending one trunkline into connection with another.

What I claim as my invention is:

1. In a telephone system, a line, a series of trunks, an automatic switch individual to said line for connecting the same with an idle trunk, said switch having a single ma net core provided with a plurality of ings thereon, a circuit including both sides of the line in series ior energizing one of said windings, and a local circuit for energizing another of said windings In a telephone system, a subscribers line, a series of an automatic switch for automatically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core having a plurality of windings thereon, a circuit including the two sides of said line in series for energizing one of said windings when the subscriber (sills, and a one of said trunks, said switch provided with a single magnet spool having a plurality of windings thereon, a circuit for energizing one of said windings including the two sides of said line in series, a local circuit for energizing another of said windings, and a circuit including a conductor of one of said trunks for energizing a third winding.

-:L In a telephone system, a line, a series of trlmks, an automatic switch for automatically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core having a plurality of windin s thereon, a circuit including a conductor of said line for energizing one of said windings, which circuitis controlled by the magnet, and a local circuit for energizing another of said winda 5. In a telephone system, a line, a series of trunks, an automatic switch for establishing connection between said line and an idle one of said trunks, provided with a three-wound magnet, a circuit for energizing one of said windings including a conductor of said line, a local circuit for energizing another of said windings, and a circuit in cluding a conductor of one of said trunks :Eor energizing a third windin 6. In a telephone system, a e, a series of trunks, an automatic switch individual to said line for connecting the same with an idle trunk, said switch having a single ma net core provided with a plurality of windings thereon, a circuit including both sides of the line in series for energizing one of said windings, a local circuit for energizing another of said windings, and an armature for said magnet responsive to the energizing of said first to close the local circuit of said other Winding.

7. In a telephone system, a subscribers line, a series of trunks, an automatic switch for automatically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core having a plurality of windings thereon, a circuit including the two sides of said line in series for energizing one of said windings when the subscriber calls, a local circuit for energizing another 0! said Windings, and an armature for said magnet rcsponsive to the energizing of said first windina to close the local circuit of said other winding.

8. In a telephone system. a line, a series of trunks. an automatic switch for establishing connection between said line and an idle one of said trunks. said switch provided with a single magnetspool having a plurality of windings thereon. a circuit for energizing one of said windings including the two sides of said line in series, a local circuit for energizing another of said windings, a circuitincluding a conductor of one of said trunks nuances for energizing a third winding, and an armature for said magnet responsive to the energizing of said first winding to close the local circuit of said other 9. In a. telephone system, a line, a series of trunks, an automatic switch for automatically establishing connection between said line and an idle one of said trunks, said switch provided with a single'magnet core having a plurality of win' thereon, a circuit including a conductor 0 saidline for ener izing one of said windings, a. local circuit or energizin another of said and an armature or said magnet to the enelgizhig'ofsaid'first close the local circuit of said m 10. In a telephone system, a line, a series of trunks, an automatic switch individualt'o said line for connecting the same with an idle trunk, said switch having a siuglemagnet core provided with a plurality of windings thereon. a circuit including botlr sides of the line in series for energizingone of said a local circuit 'for energizing another of said windings, and as many armatnres for said magnet as there are winding thereon.

II. In a telephone system, a subscribers line, a series of trunks, an automatic switch for automatically establishing connection between said line and an idle one ofsaid trunks, said switch providedwith a single magnet core having a: plurality of thereon, a circuit including'the two sides of said line in series for energizing one of said. windings when the subscriber calls, a local circuit for energizing another of said windings, and-as many annatures for said magnet as there are windings thereon.

12. In a telephone System, a line, a; series oftrunks, an automatic switch for establishing connection between said line and an idle one of mid said switch provided with a single wool having a pluralit of windings thereon, a circuit for energizing one of said including the two sides of said 'line in series a local circuit for energizing another of said windings,- a circuit including a conductor of one of'seid trunks for energizing a third winding, and as many armatures for said magnet as there are thereon.

13. hi a telephone system, a line, a series of trunks. an automatic switch for automatically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core having a plurality of thereon. a circuit includinga conductor ofsaid line for energizing one of said i P's, a local circuit for another of and asmnnyannature's for said magnet as there are'windings thereon.

14. In a telephone systenn a line, a series of t'fuuks, an automatic switch for establishingconnection between said line and an idle one of said trunks, a circuit for energizing one of said windings including a conductor of said line, a local circuit for energizing another of said windings, a circuit including a conductor of one of said trunks for energizing a third winding, and as many armatures for said magnet as there are windings thereon.

15 In a telephone system, a line, a seriesof trunks, an automatic switch individual to saidline for connecting the same with an idletrunk, said switch having a single'magnet'spool provided with a plurality of windings thereon, a circuit including both' sides of the line in series for energizing one of said windings, a local circuit forienergizing another of said windings, and a circuit-closing plunger operated by the closure of said local circuit.

16. In a telephone system, a subscrihers line, a series of trunks, an automatic switch for automatically establishing connection between said line and an idle' one of said trunks said switch provided with a: single magnet spool having a plurality of windings thereon; a circuit including the; two sides of said line in series for energizing one of said windings whena the subscriber calls, a local circuit for energizing another of said windings, and a plunger operated by the closure of saidilocal circuit.

17. In: a: telephone system, aline, aseries of trunks, an automatic switch for establishing connection between saidlineand an-idle one of said trunks, said switch pronided with a single-magnet spool having a plurality of windings thereon, a circuit for energizing ne'of said windings including the two sides of said line in' series, a local circuit for ener another of'said windings, a circuit including a conductor of one of'said trunks-for energizing a third and a circuit-closing plunger operated by the closure of said local circuit.

18. Ina telephone system, a line, a series of trunks, an automatic switchfor automatically establishing-connection between said lineand an idle one of said trunks, said switch provided with a single magnet spoolv havinga plurality of windings thereon, a circuit including a conductor of said line for energizing one of said windings, a local circuit for energizing another of said windings, and a circuit-closing plunger operated by the closure of said local circuit.

19. In a telephone system, a line, a series of trunks, an automatic switchfor-establishing connection between said line, and an idle one of said trunks, a circuit for energizing one of said windings including a conductor of said line, a local circuit- :Eor-ener gizing another of said windings, a circuit including a conductor of one of said trunks for energizing a third winding, and a circuit-closing plunger operated by the closure of said local circuit.

20. In a telephone system, a line, a series of trunks, an automatic switch individual to said line for connecting the same with an idle trunk, said switch having a single magnet core provided with a plurality of windings thereon, a circuit including both sides of the line in series for energizing one of said a local circuit for energizing another of said windings, and a battery or centralized means of lament-supply for furmshmg' current to sai circuits or operating purposes, and over said line to the calling substation for talking purposes.

21. In a telephone system, a subscribers line, a series of trunks, an automatic mtch for automatically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core having a plurality of windings thereon, a circuit including the two sides of said line in series for energizing one of said windings when the subscriber calls, a local circuit for energizing another of said windings, and a battery or centralized means of current-supply for furnishing current to said circuits for operating purposes, and over said line to the calling substation for In a telephone system, a line, a series of trunls, an automatic switch for establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet spool having a plurality of windings thereon, a circuit for enerone of said including the two sides of said line in series, a local circuit for energizing another of said windings, a circuit including a conductor of one of said trunks for energizing a third winding, and a battery or centralized means of currentsupply for furnishing current t5) said cir cuiisforopera' 'p an oversai line to the cal ling su bstation for talking p 23. In a telephone system, a line, a series of trunks, an automatic switch for automatically establishing connection between said line and an idle one of said trunks, mid switch provided with a single magnet core having a plurality of windings thereon, a circuit including a conductor of said line for energizing one of said windings, a local circuit for energizing another of said Windings, and a battery or centralized means of current-supply for furnishing current t3 said circuits for operating purposes, an

over said line to the calling substation for talking purposes.

24. In a telephone system, a line, a series of trunks, an automatic switch for establish ing connection between said line and an idle one of said trunks, provided with a threewound magnet, a circuit for energizing one of said windings including a conductor of said line, a local circuit for energizing another of said windings, a circuit including a conductor of one of said trunks for energizing a third Winding, and a battery or centralized means of current-supply for furnishing current to said circuits for operating purposes, and over said line to the calling substation for talking purposes.

25. In a telephone system, a. line, a series of trunks, an automatic switch for establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet spool having three windings thereon an armature for each winding, a line circuit for energizing one winding, a local circuit closed by the armature of the one winding for energizing another winding, a swinging and endwisemovable circuit-closing plunger operated by the energizing of the said other winding, and a circuit includin a trunk conductor for energizing the winding, the armature of the third winding controlling the circuitlgf the; orlzle winding. hn

26. a te ep one system, a e, a magnet for said line, three windings on said magnet, two armatures for one end of said magnet, a single armature for the other end of said magnet, a traveling plunger operated by one of the two armatures, the circuit through one of said windings controlled by said plunger, and line and local circuits for the other two windings, the line circuit controlled by the other of the said-two armatures, said third armature controlling said local circuit.

27. In a telephone system, a magnet individual to the subscribers line having three windings, each winding controlled by a different circuit, and each winding a. separate armature, together with switching means controlled by said armatures.

-28. In a telephone system, a line, a. series of trunks, and an automatic switch for antomatically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core for controlling both the operation and the release of said switch, said magnet being provided with a plurality of one of said windings adapted to control the operation of said switch and another to control the release of the same after operation thereof.

29. In a telephone system, a line, a series of trunks, and an automatic switch for antomatically establishing connection between said line and an idle one of said trunks. said switch provided with a single magnet core for controlling both the operation and the release of said switch, said magnet being provided with a plurality of windings, one of said windings adapted to control the operation of said switch and another to control the release of the same after operation thereof, said release winding being energized over a circuit including one of said trunks.

30. In a telephone system. a line. a series of trunks, an automatic switch for auto matically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core for controlling both the operation and the release of said switch. said magnet being pron'ded with a plurality of windings, one of said windings adapted to control the operation of said switch and another to control the release of the same after operation thereof, and means for controlling the operation of said magnet over two sides of the line in series.

31. In a telephone system, a line, a series of trunks, an automatic switch for auto matically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core for controlling both the operation and the release of said switch, said magnet being provided with a plurality of windings, one of said windings adapted to control the operation ofsaid switch and another to control the release of the same after operation thereof, said release winding being energized over a circuit including one of said trunks, and means for controlling the operation of said magnet over two sides of the line in seria.

32. In a telephone system, a line, a series of trunks, an automatic switch for automatically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core for controlling both the operation and the releam of said switch, said magnet being provided with a plurality of windings, one of said windings adapted to control the op eration of said switch and another to control the release of the same after operation thereof, and a battery or centralized means of current-supply for furnishing current to said for operating purposes, and over said line to the calling substation for talking purposes.

33. In a telephone system, a lme, a senes of 1 an automatic switch for automatically establishing connection between said line and an idleone of said trunks, said switch provided with a single magnet core for controlling both the operation and the release of said switch, said magnet being provided with a plurality of winding, one of said windings adapted to control the operation of said switch and another to control the release of the same after operation thereof, said release winding energized over a circuit including one of said trunks, and a battery or centralized means of current-supply for furnishing current to said circuits for operating purposes, and over said line to the calling substation for talkingnpurposes.

34. a telephone system, a line, a series of trunks, an automatic switch for auto matically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core for controlling both the operation and the release of said switch, said magnet being provided with a plurali of winding, one of said windings adapte to control e operation of said switch and another to control the release of the same after operation thereof, means for controllin the operation of said magnet over two si es of the line in series, and a battery or centralized means of current-sup ly for furnishing current to said circuits or operating purposes, and over said line to the calling substation for talking purposes.

35. In a telephone system, a line, a series of trunks, an automatic'switch for automatically establishing connection between said line and an idle one of said trunks, said switch provided with a single magnet core for controlling both the operation and the release of said switch, said In at being provided with aplurality of one of said adapted to control e operation ofsaid switch and another to control the release of the same after operation thereof, said release being encrgized over a circuit'including one of said trunks. means for contro the operation of said magnetforer two si es of the line in series, and ahattery orcentralized means of Salient-supply for current t3 sai circuits or operating purposes, an over said line to the calling substation for purposes.

36. a telephone system, a line, a series of trunks, an automatic switch for auto matically establishing connection between a said line and an idle oneiof said trunks, a

magnet core for said switch, a pair of windings on said magnetcore having the same magnetic circuit and adapted .to control the operation and release of said switch, and a third winding onj'said core ha asepwin ate magnetic circuit and adap to control the circuit through one of said firstmentioned 37. In a telephone system, a line, a series 'of trum an automatic switch for automatically establishing connection between said line and anidle one of said trunks, a magnet core for said switch, a pair of windings on said magnet core having the same magnetic circuit and adapted to control the operation and release of said switch, a third winding on said core having a separate magnetic circuit and adapted to control the circuit through one of said first-mentioned windings, and means for one said third winding over two sides of the e in series.

38. In a telephone system, aline, a series of trunks, an automatic switch for automatically establishing connection between said line and an idle one of said trtmks, a. magnet core for said switch, a pair of windings on said magnet core, a relay, and means for energizing said relay in series with one of said windings to thereby close a circuit through the second of said windings.

39. In a telephone system, a line, a series of trunks, an automatic switch for automatically establishing connection between said line and an idle one of said trunks, a magnet core for said switch, a pair of windings on said magnet core, a relay, and means for energizing said relay in series with one of said windings over two sides of the line in 40. In atelephone system, a line, a. series of trunks, an automatic switch for automatically establishing connection between said line and an idle one of said trunks, a. magnet core for said switch, a pair of windings on said magnet core, a relay, means for energizing said relay in series with one of mid windings to thereby close a circuit throu h the second of said windings, and a secon relay adapted to be energized in multiple with said second upon the energization of said first relay to thereby interrupt the energizing circuit of said fiistmentioned relay and winding.

41. In a telephone system, a line, a series of trunks, an automatic switch for automatically establishing connection between slid line and an idle one of said trunks, a. magnet core for said switch, apair of windings on said magiet core, a relay, means for energizing said relay in series with one of said windings over two sides of the line in serfs, and a second relay adapted to be energized in multiple with said second windingupon the energization ofsaid first relay; to thereby interrupt the energizing cirof said first-meutioned relay and wind- 4.2. In a telephone system, a line, a plurality oftrunks acossible thereto at a. central ofiioe, a nonnumerical automatic trunking switch for saidlline, means for operating the switch for connecting the line with an idle trunk, said means comprising a magnet, a circuit for said magnet comprising two control points, control means at each point having having difierent time instants for closing one point before the 43. In aeteleplione system, a line, a. plurality of trunks accessible thereto at a central ofiice, a non-numerical automatic trunking switch for said line, means for operating the switch for connecting the line with an idle trunk said means comprising a magnet, a circuit for said magnet comprising two control points, one in the line and one in the central olfice, control means at each pointhaving different time constants.

1-1. In a. telephone system, a line, a plurality of trunks accessible thereto at a central ofiice, a non-numerical automatic trunking switch for said line, means for operating the switch for connecting the line with an idle trunk, said means comprising a. magnet, a circuit for said magnet comprising two control points, one in the line and one in the central oflice, control means at each point having different time constants for holding one point open longer than the other.

45. In a telephone system, a line, a plu rality of trunks accesible thereto at a central oilice, an automatic trunking switch for said line, means for operating the switch for connecting the line with an idle trunk, said means comprising a line relay, a circuit for said relay and a plurality of means for controlling said circuit having difierent time constants.

46. In a telephone system, a line, a plurality of trunks accessible thereto at a central ofiioe, an automatic trunking switch for said line, means for operating the switch for connecting the line with an idle trunk, said means comprising a line relay, a circuit for said relay comprising two control points, control means at each point having difierei; timzlcoilistants. 1mg In 47. a eponesystem,a aprality of trunks aocesible thereto at a central ofiice, an automatic trunking switch for said line, means for operating the switch for connecting the line with an idle trunk, said means comprising a line-relay, a circuit for said relay comprising two control points, control means at each point having difi'erent time constants for closing one point before the other.

4 8. In a telephone system, a line, a pluof trunks accesible thereto at a central ollice, an automatic trunking switch for said line, means for operating the switch for-connecting the line with an idle trunk, said means comprising a. line relay, a circuit for said relay comprising two control points, one in the line and one in the central ofiice. the control means at each point havmg dlfi'erent time constants 49. In a telephone system, a line, a. plurality of trunks accessible thereto at a central ofl ice. an automatic trunking switch for 831d lme, means for operating the switch for connecting the line with an idle trunk, said means comprising a line relay, a circuit for said relay comprising points, one In the line and one in the central two control oflice the control means at each point having different time constants for holding one point open longer than the other.

50. In a telephone system, a plurality of lines, a plurality of trunks common to said lines at a central office, a trunk selecting device for said lines comprising means common to all the lines and means individual to each line, a magnet for one of said lines,

19 a circuit for said magnet having two control points, said common means controlling one and the individual means controlling the other, said common and individual means having different time constants Signed by me at Chicago, Cook county, is

Illinois, this 520th day of August, 1908.

ALEXANDER E. KEITH. \Vitnesses EDWARD D. FALEs, ETHEL A. EDGELL.

It is hereby certified that in Letters Patent No. 1,151,543, granted August 24,

19l5, upon the application of Alexander E. Keith, 01' Hinsdale, Illinois, for an improvement in Telephone-Exchange Trunking Systems," errors eppear in the printed specification requiring correction as follows: Page 5, line 13, for the word attached road attracted; same page, line 126, for the word the read this; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 7th day of December, A. D., 1915.

[SEAL-1 R. F. WHITEHEAD Acting Commissioner of Patents. 

